Sickle cell disease (SCD) is characterized by painful vasoocclusive crises that occur on top of a chronic, progressive vascular disease. Advancement towards new treatment modalities for SCD has been significantly hampered by the lack of biomarkers that can effectively monitor the underlying pathophysiological processes. We have previously shown that SCD subjects have marked dysregulation of the autonomic nervous system (ANS), and that sigh and pain can cause vasoconstriction. We hypothesize that physiologically-based biomarkers reflecting regional perfusion and ANS balance report the collective effects of all molecular and cellular pathologies secondary to the gene defect in SCD. To study this hypothesis, we have assembled a group of skilled investigators from multiple disciplines (pain and behavioral research, biomedical engineering, cardiology, chemistry, hematology, physiology and biophysics, pulmonology, and radiology) to develop and calibrate biomarkers reflecting 1) cardiac ANS imbalance, peripheral and pain-triggered vasoconstriction; and 2) peripheral vascular function and regional cerebral flow and oxygenation. Another goal is to provide standardized measurement/processing tools for use by others. Our unique approach involves sampling multiple physiological variables simultaneously and using computational modeling to account for the complex interactions and isolate the biophysical biomarker of interest. Measurements will be made in human subjects with selected hematological disorders that differ in degree of anemia or blood rheology. We will also study SCD patients on chronic transfusion with varying percent hemoglobin S in order to separate the measurement components due to altered blood rheology and cardiac output from the components reflecting vascular status and the autonomic function of interest. The translation of these biomarkers and derived tools to the SCD research community will fulfill a need and be invaluable for stratifying risk, monitoring disease status, an measuring the effects of therapeutic interventions in patients with SCD. In the course of validating these biomarkers, we will improve our understanding of vascular disease in SCD and other hemoglobinopathies, as well as in normal subjects. (End of Abstract)